(1) Field of the Invention
The present invention relates to an image reading method and an image reading apparatus used for reading not only a color image (a multicolor image) but also a single color image (a monochormatic color image) with a color image pickup unit such as a color CCD.
With an improvement of a performance of an information processing apparatus such as a personal computer or an increase of a capacity of a storage medium such as a magneto-optic disk, an electronic filing system for reading, storing and retrieving an image has been spreading in recent years. For this, there is a demand for an image reading apparatus such as an image scanner which can read an image at a high speed. In addition to this, there is also a demand for an image reading apparatus which can efficiently read an image at a high speed in the case of both a monochromatic color image and a multicolor image.
(2) Description of the Related Art
FIG. 10 is block diagram of an image reading apparatus known in the art. In FIG. 10, reference numeral 100 denotes a color CCD, 200 denotes a white fluorescent lamp, 300 denotes a personal computer (PC), 400 denotes a lighting control unit, 500 denotes an image that is an object to be read such as an original.
The color CCD 100 reads the image 500 with reading wavelengths of three colors of red (R), green (G) and blue (B), and outputs it as read data of three colors (an RGB output).
The white fluorescent lamp 200 generates a white light containing light of all the above three wavelengths, and radiates it on the image 500. The personal computer 300 performs a reading process on the basis of the data output from the color CCD 100.
The lighting control unit 400 controls ON/OFF of the white fluorescent lamp 200 according to a signal for initiating or terminating the reading process on an image from the personal computer 300.
The image reading apparatus known in the art with the above structure radiates a light from the white fluorescent lamp 200 onto the image 500, receives a reflected light with the color CCD 100, obtains image data of three colors (R, G and B) of the image 500 from the received light on the basis of spectral characteristics of three colors of red (R), green (G) and blue (B), performs a necessary process such as amplification, A/D conversion, etc., and outputs it to the personal computer 300.
The personal computer 300 performs a reading process based on the image data of all three colors if the image 500 is a multicolor image (that is, in the case of a multicolor reading). If the image that is an object to be read 500 is a monochromatic color (a single color image) (in the case of a monochromatic color reading), the personal computer 300 performs a reading process based on the image data of any one of the images of these three colors.
There is another apparatus which performs a reading process to read an image (an image that is an object to be read 500) with a monochromatic color CCD 100A, three fluorescent lamps a red fluorescent lamp (R) 200A, a green fluorescent lamp (G) 200B and a blue fluorescent lamp (B) 200C and a lighting control unit 400A, instead of the above color CCD 100, the white fluorescent lamp 200 and the lighting control unit 400, as shown in FIG. 11.
The monochromatic color CCD 100A receives a light from the image 500, and outputs read information of a single color. The fluorescent lamps 200A through 200C generate a light of red (R), green (G) and blue (B), respectively, and radiate the light on the image 500.
The lighting control unit 400A controls the three fluorescent lamps 200A, 200B and 200C to be successively switched or lighted simultaneously, as described later, according to an instruction of a multicolor reading or a monochromatic color reading input from the personal computer 300.
In the image reading apparatus shown in FIG. 11, if the image 500 is a multicolor image, the lighting control unit 400A successively switches lighting conditions of the three fluorescent lamps 200A, 200B and 200C in order of, for example, the red fluorescent lamp 200A.fwdarw.the green fluorescent lamp 200B.fwdarw.the blue fluorescent lamp 200C, whereby only one light among three colors of R, G and B is successively radiated on the image 500. The monochromatic color CCD 100A reads the image 500 by receiving a reflected light in any one color among the three colors of R, G and B from the image 500, and outputs obtained image data one color by one color to the personal computer 300 to perform the reading process.
If the image 500 is a monochromatic color image, the lighting control unit 400A controls the three fluorescent lamps 200A, 200B and 200C to be lighted simultaneously to radiate the light of all three colors of R, G and B onto the image 500, and the monochromatic CCD 100A receives a reflected light and outputs image data to the personal computer 300 to perform a reading process. In this case, simultaneous lighting of the three fluorescent lamps 200A through 200C allows an increase in quantity of light, and increasing an illuminance of the reflected light from the image 500 so as to shorten a time required to store an electric charge in the monochromatic color CCD 100A to permit a reading process at a rate higher than that of a multicolor reading.
Even in the case of the monochromatic reading, the image reading apparatus shown in FIG. 10 performs the same reading process as the multicolor reading to obtain image data of three colors to read the image 500 on the basis of the image data of only one color. This image reading apparatus shown in FIG. 10 has therefore a disadvantage that a processing of the monochromatic reading, which is considered that the reading process must be quicker than the multicolor reading, is performed at the same rate as the multicolor reading.
In the image reading apparatus shown in FIG. 11, three fluorescent lamps 200A, 200B and 200C are simultaneously lighted so that the monochromatic reading may be performed at a rate higher than the multicolor reading. However, the three fluorescent lamps 200A, 200B and 200C are successively switched to ON and OFF upon the multicolor reading. As a result, nothing can prevent a light of a color of the fluorescent lamp that was lighted immediately before from remaining.
If a time interval of the lighting of the fluorescent lamps 200A, 200B and 200C is shortened too much, the monochromatic CCD 100A receives together an afterglow of another color of fluorescent lamp that was lighted immediately before although the monochromatic CCD 100A ought to receive a light of only, for example, green color. This makes it difficult to obtain accurate image data. In consequence, there is a limitation to shorten a time interval of lighting of the fluorescent lamps 200A, 200B and 200C in order to increase a processing rate of a reading.
In the case of a multicolor reading, the three fluorescent lamps 200A, 200B and 200C are required to be switched ON and OFF quite frequently until an end of the reading process. This leads to short service lives of the fluorescent lamps 200A, 200B and 200C.